What Is an Animal?

Name ______

What is an Animal?

That might seem like an odd question, but if we are going to classify them, we really ought to decide if they belong in the animal group in the first place. Animals are living organisms. This means they breathe, they eat, they grow and they reproduce (make more like themselves). Plants are living organisms, too. So, what is the difference between a plant and an animal? The biggest difference is that most plants do not move, whereas most animals do. The true difference, though, is that plants produce their own food, whereas animals feed off other things.

Bones or No Bones?

Once you have decided you have an animal, you need to decide where to put it. The Animal Kingdom is divided up into groups. Every animal belongs in a special place, sort of like an address. The first two groups are the vertebrates and invertebrates. The invertebrates are animals with no bones. These include insects, spiders, and other groups for things like crabs, jellyfish, oysters, earthworms and more. The vertebrates, or animals with bones, can be divided into five main groups. These are mammals, birds, fish, reptiles and amphibians.

Invertebrates (no bones)

We are only going to look at two groups of invertebrates. Spiders and insects. Many people thing that spiders are insects, but they are wrong.

Insects have three main body parts and six legs.

Spiders have two main body parts and eight legs.

Vertebrates (have bones)

There are five main groups. These groups can be split further, into warm-blooded and cold-blooded animals. A warm-blooded animal is like you and me. It keeps its body temperature the same, unless it is sick. Cold blooded animals don't keep their body temperatures the same, it changes according to the surroundings. So if the weather is hot, the animal is hot, and if the weather is cold, it is cold.

Warm-blooded:

Mammals:

Have hair or fur

Breathe air

Feed their young milk

Whiskers are a type of hair, so just having whiskers counts as having hair or fur.

Birds:

Have wings and feathers

Breathe air

Lay eggs

Cold-blooded:

Fish:

Have scales, fins and tails

Breathe underwater (using gills)

Reptiles:

Have dry skins and scales

Breathe air

Lay eggs

Amphibians:

Have smooth wet or slimy skins

Spend part of their life in water and part on land